Cellular Telephones Original Mobile Telephones One transmitterreceiver Limited

Cellular Telephones • Original Mobile Telephones – One transmitter/receiver – Limited number of channels – For good service can support about 20 subscribers per channel (rough rule of thumb) Mobile Phone Transmitter/ Receiver

Cellular Telephones • Divide Region into Cells – One cellsite (transmitter/receiver) per cell – Channels can be reused in non-adjacent cells Uses Channel 232 Used in 4 cells Yes Can Reuse Ch. 232? No No No Yes No No No

Cellular Telephones • Channel Reuse – Without channel reuse, you can serve only about 20 subscribers per channel for good service – Rough rule of thumb – Otherwise, the system will not be available too often when people want to call or receive calls

Cellular Telephones • Channel Reuse Rule – How many times can we reuse each channel in an area? – Channel reuse factor = Number of cells / 7 – If 20 cells, reuse factor is about 3 (round off) – Can reuse each channel about 3 times – Rough rule of thumb

Cellular Telephones • Capacity Calculation – If 100 channels and 15 cells – 100 channels – x 20 subscribers per channel – x 15/7 channel reuse factor – = about 4, 000 subscribers (100 x 2)

Handoffs • When you move to another cell within the same system, you get a handoff – You are transferred automatically to that cell’s cellsite

Roaming • Roaming is when you take your cellphone to another city – Use it there to send and receive – Not always possible technically because of incompatible cellular technology – May be limited procedurally because of high rates of cellular fraud in some areas – Don’t confuse this with handoff, which takes place within a cellular system between cells

Control • Mobile Telephone Switching Office – Controls cellsites, handoffs, etc. – Calls go to/from MTSO – Connects to POP to link to traditional telephone (wireline) carriers POP MTSO ILEC, ICX, etc.

Placing a Call • • New Enter number, hit send Cellphone broadcasts request Several cellsites receive, send to MTSO assigns cellphone to cellsite where signal is loudest • MTSO sends message to cellphone via that cellsite, telling the phone what incoming, outgoing channels to use

Receiving a Call New • MTSO has each cellsite broadcast cellphone’s ID number • Cellphone transmits a response • Responses from cellsites go to MTSO • MTSO selects cellsite where signal is loudest • MTSO sends message via the cellsite to cellphone, giving channels and telling the cellphone to ring

First Generation Cellular • Analog or Digital Operation – Initially analog; U. S. States initially was analog using the AMPS standard • Limited use of digital Cellular Digital Packet Data (CDPD) standard – Europe and the rest of the world started with a large number of incompatible analog systems but settled on the digital GSM standard

First-Generation Cellular • Large Cells – Usually only 20 -40 per city – Limits channel reuse • Limited Number of Channels – In U. S. , 832 two-way channels • No Compression – Each voice signal required a full two-way channel

First-Generation Cellular • How Many Subscribers Can You Support? – – – – 20 cells Channel reuse is about 3 (20/7) 832 channels With channel reuse, 2, 496 effective channels 20 users per available channel So only about 50, 000 subscribers per city Engineering tricks can extend, but only somewhat

Second-Generation Cellular • Personal Communication Service (PCS) – Or Personal Communication Network (PCN) • More channels – About 2, 500 • Smaller cells permit more channel reuse – Don’t just say “smaller cells; ” be explicit about channel reuse • Compression of around 3: 1 – Supports more subscribers per channel

Second-Generation Cellular • Digital – Cleaner signal – Paging and other digital services – Internet access

Potential System Capacity (Roughly) • Category 1 st Gen • Cells/City 30 2 nd Gen 100 • Channel reuse (cells/7) ~4 • Channels 800 ~14 2, 500 • Effective channels 3, 200 35, 000 • With compression *3, 200 • Subscribers (x 20/channel) 2, 000 105, 000 64, 000 • *No compression in 1 st generation

Second-Generation Cellular • PCS Cellphones – Do not have to transmit as far because cells are smaller • Inverse cube law--if triple distance, 33 or 27 times the power required • Cellphones can be less expensive because less power

Second-Generation Cellular • PCS Cellphones – Large number of possible subscribers removes scarcity cost penalties – But vendors try to avoid simple price competition by offering more services made possible by digital technology

Second-Generation Cellular • Most of World – Standardizing on DCS Technology – Based on GSM and usually called GSM • U. S. – – – FCC did not specify a standard! Different carriers use different technologies Some have standardized on GSM Your cellphone may not work with another carrier Limits roaming

Generations: Recap Analog/Digital Cells 1 st Both A&D 2 nd Digital Large Small Channels (Approx. ) 800 2500 Compression No Yes U. S. Standardization AMPS Poor International Standards GSM DCS

Second-Generation Cellular New • Data – Initially limited to about 10 kbps – 100 kbps coming over second-generation systems in some countries

Third-Generation (3 G) • Smarter Devices – Devices will have the power of a small PC • Greater Number of Uses – Data, including internet access – Graphics and even video • International Mobile Telecommunications (IMT) – European-led standard for 3 G generation cellular

Third-Generation (3 G) Cellular • Data – Up to 3 Gbps New